1. Field of the Invention
The present invention relates to a method to produce an optical transceiver that implements with a semiconductor laser diode (hereafter denoted as LD).
2. Related Background Arts
An optical transceiver generally installs a semiconductor laser diode (hereafter denoted as LD) as an optical source. Various prior arts have been disclosed methods to control the LD, where the methods keep the average optical power of the light output from the LD substantially in constant and the extinction ratio of the light also substantially in a preset range. Specifically, the optical transceiver prepares a temperature sensor, a look-up-table (hereafter denoted as LUT) which relates parameters for the LD with temperatures, and a controller. The controller, as referring to the LUT, adjusts the bias current and the modulation current each supplied to the LD.
In order to create such a LUT, various characteristics of the LD against the temperature are necessary. Generally, the average output power of the LD is kept substantially in constant by adjusting the bias current by an automatic power control (hereafter denoted as APC) circuit. However, the extinction ratio (ER), which is given by a ratio of the high level to the low level of the light output from the LD, namely, ER=10×log {P(1)/P(0)}, is conventionally adjusted only by setting the modulation current stored in the LUT. Because the extinction ratio depends on the temperature, the LUT is necessary to store many data for respective temperatures.
On the other hand, the measurement of the temperature dependence of the modulation current needs complex procedures. That is, the temperature of the optical transceiver is necessary to vary the ambient temperature. However, it takes longer time until the temperature of the LD in the optical transceiver becomes substantially equal to the ambient temperature of the optical transceiver. The characteristics of the LD measured in advance to the installation thereof within the optical transceiver, and it is very hard to regards the characteristics of the LD as performances of the optical transceiver. Accordingly, it is preferable to measure the performances of the LD at several temperatures and create a table, which is often called as a look-up-table (LUT), to convert the performances to those under general temperatures. Because of the discrepancy of the ambient temperature and that of the LD when the LD is enclosed within the optical transceiver, the LUT often lacks the accuracy. A technique to enhance the accuracy of the LUT has been desired.